A team of Berkeley Lab battery researchers led by Elton Cairns has invented an advanced lithium/sulfur (Li/S) cell that, for the first time, offers both long cycle life and a high discharge rate in addition to the inherently low cost and light weight of Li/S batteries.
The researchers developed a sulfur-graphene oxide (S-GO) nanocomposite cathode that vastly improves the cycle life of Li/S cells by immobilizing sulfur and inhibiting polysulfides during operation. Tests show that the Berkeley Lab Li/S cell had an estimated specific energy of ~500 Wh/kg, more than double that of current Li-ion cells (~200 Wh/kg). It maintained a high capacity through 1,500 charge/discharge cycles, and also maintained capacity during high discharge and charge rates, such as those required of batteries serving cordless power tools.
In earlier Li/S cells, capacity faded rapidly due to sulfur loss from the cathode by formation of soluble polysulfides in the electrolyte during the charge/discharge cycle. The Berkeley Lab cell avoids this effect through a process that deposits sulfur on ultra-thin cathode surfaces made of nanoporous graphene oxide (GO). Modifying the S-GO composite with a cationic surfactant, CTAB (cetyltrimethyl ammonium bromide) adds a layer of protection for the sulfur attached to the GO.
In addition, a flexible adhesive, or binder, holds the cathode materials in place despite the electromechanical expansion and contraction that occurs during the charge/discharge cycle. Finally, the Berkeley Lab cell employs an improved ionic liquid electrolyte that further reduces polysulfide formation and blocks trace amounts from binding to the lithium metal anodes of the Li/S cells. The combination of features in the Berkeley Lab cell provides an unprecedented level of performance and reliability for Li/S cells.
- 1,500 charge/discharge cycles demonstrated
- High specific energy – approximately 500 Wh/kg
- High discharge and charge rates
- Li metal anode: 90 percent less weight than carbon anodes
- Low-cost, Earth-abundant materials
Applications and Industries
- Electric and plug-in hybrid vehicles
- Portable electronics, e.g., mobile phones, cameras
- Cordless power tools